> > gateway was duplicating(?) data out the PPP interface.  (Maybe it was
> > sending something else---but it was sending _something_ out the modem in
> > lockstep with the X protocol packets going to my X server.)
> 
> This smells like DNS or resolver configuration pointing your machine to
> query an external server for reverse-lookups of new connections.

It turned out that I wasn't running routed on the gateway.  The packets
going over the modem were really intended for the gateway, but were bumped
up to my ISP before echoing back to the local machine.

A fair bit of extraneous traffic was also due to Kerberos exchanges going
on.


> Have you checked for these types of problems yet?

``I am only an egg,'' as Valentine Michael Smith would say.  (^&  I only
worked out more or less what was happening when running tcpdump, per
someone else's suggestion.  But, I expected that it was some kind of
elementary networking configuration problem.


  "I probably don't know what I'm talking about." --rauch@eecs.ukans.edu